To permit our use of the electron microscope: 1. To determine if viruses or structures associated with and indicative of viral infection are present in biopsy or necropsy tissues and in tissue culture lines established from patients with chronic degenerative diseases. 2. To determine the ultrastructure of the major structural proteins and antigens of the coronavirus virion and to aid in the evaluation of the effectiveness of organ culture systems to detect and identify agents from acute respiratory diseases. 3. To monitor culture materials for the presence of viral particles in organ culture systems infected with the etiologic agent of viral hepatitis types A and B. 4. To determine the structure and morphology of the complement-fixing and precipitating antigens of rubella virus and to determine the relationship of these antigens to the infectious virus particle. 5. To study the pathogenesis of Colorado tick fever virus in bone marrow in man and experimentally infected mice.